Polymer materials, e.g. polyolefin materials such as ethylene polymers generally have rather poor resistance to the influence of different environmental conditions such as light, heat and weather.
To improve the physical properties of polymer materials and to increase their resistance to the influence of environmental conditions, various stabilizing additives are usually added in a total amount of about 0.05-5% by weight, preferably about 0.1-4% by weight. These additives include antioxidants such as sterically hindered phenols, aromatic amines, organic phosphites, and thio compounds; and light stabilizers such as hindered amine light stabilizers (HALS). Usually a “cocktail” of at least two different stabilizing agents, e.g. a HALS compound and a hindered phenol compound is added to the polymer material. However, known stabilizing additives often have an insufficient stabilizing effect or become unsatisfactory due to bleeding of the additive from the polyolefin material. A stabilizing additive that effectively protects polymer materials against the influence of environmental conditions and which is not prone to bleeding from the polymer material would therefore be desirable.
One such stabilizing additive is disclosed in EP-A-0 468 418 and consists of a copolymer of ethylene (A) and a vinyl compound (B) represented by the general formula: wherein R1 and R2 are each an independent hydrogen atom or a methyl group, R3 is a hydrogen atom or an alkyl group of 1-4 carbon atoms; a ratio of (B) to the sum of (A) and (B) is less than 1 mol %; a proportion of the amount of vinyl compounds (B), which are not successively bonded to like units (B) in the chain, but bonded to unlike units (A) on both sides thereof, to the total amount of (B) units in the copolymer is at least 83%; and an MFR of the copolymer ranges from 0.1 to 200 g/10 min.
In EP-A-0 468 418 it is submitted that decreased light stability of hindered amine copolymer additives is caused by the block structure comprising at least two vinyl moieties successively bonded having hindered amines in the side chain or unreacted residual ester groups. The most important feature of EP-A-0 468 418 is therefore said to be that the proportion of the amount of vinyl compounds (B) which are not successively bonded at all to like units (B) in the chain to the total amount of (B) is at least 83%. Consequently, the ratio of the vinyl compound (B) to the sum of ethylene (A) and the vinyl compounds (B) is less than 1 mol %.